Many yo-yo tricks require the yo-yo to spin freely at the end of the string without climbing up the string. A yo-yo spinning freely at the end of the string is commonly said to "sleep" or "dwell." Ideally, a player will cause the yo-yo to sleep, and perform the desired trick while the yo-yo is spinning. After the trick has been executed, the player tugs on the string and the yo-yo climbs up the string again (referred to herein as "waking up" the yo-yo). While it becomes increasingly easier to make the yo-yo sleep as the friction forces between the string and yo-yo axle are decreased, it also becomes increasingly more difficult to wake up the yo-yo and cause it to climb up the string from a sleeping condition. Thus, the friction forces between the string and axle must be adjusted to accommodate the skill level of the player and the types of tricks performed.
The string gap is the distance between the two yo-yo body halves. A decrease in string gap will typically make winding the string around the axle easier, and will also make waking up the yo-yo easier. In known yo-yos, the string gap may be adjusted by rotating the body halves with respect to each other, as a threaded connection between the axle and one of the body halves causes the body halves to be drawn together or moved apart. Setting the string gap to the proper setting often requires trial and error on the part of the player. Many players have their own preferred string gap setting.
It is also known to include a bearing on the axle and to interconnect the string to the bearing to reduce friction forces between the axle and the string. Many bearings create a state of very low friction around the axle, making it difficult to wake up the yo-yo. Small amounts of heavy lubricant (e.g., grease, petroleum jelly, etc.) having relatively high viscosity are often introduced around the bearing to increase the friction of the bearing to a level at which the yo-yo can sleep for a time sufficient to execute a trick, but at which the yo-yo is still relatively easily woken up. By balancing the string gap setting and the amount of lubricant around the bearing, a player can optimize the ease with which the yo-yo is put to sleep and woken up.